Anode and alloy for making same



- 33 I g I 4 l 13 v I 33 a9 7 6 v Zed Jazz 22 y 1941- z. J. ATLEE2,250,322

ANODE AND ALLOY FOR MAKING SAME Filed March 6, 1939' Patented July 22,1941 UNETE STATES PATENT OFFICE ANODE AND ALLOY FOR MAKING SAME.

Application March 6, 1939, Serial No. 260,004

3%) Claims.

This invention relates in general to the production of X-rays, and hasmore particular reference to anodes and anode material for use in X-raygenerators and like equipment.

An important object of the invention is to provide an improved anodecharacterized by the ability to stand up under the relatively hightemperatures to which the same is exposed in service during theoperation of the X-ray generator, without failure due to cracking.

Another important object is to provide an improved alloy materialparticularly well adapted for use in the formation of anodes, havinghigh heat conductivity and relatively small grain, and

consequently highly resistant to the development 7 of cracks whenheated.

Another important object resides in providing an improved method oftreating a copper alloy, whereby to precipitatela medium between thegrain boundaries of the alloy whereby to increase the hardness andtensile strength, the method serving also to inhibit grain growth uponheating of the alloy, whereby to provide 2. preferably copper alloyparticularly well adapted for high temperature service and in whichthere is little, if any, tendency toward cracking of the material due tograin growth when heated excessively.

These and other objects of the invention will become apparent from thefollowing description, which, taken in connection with the accompanyingdrawing, discloses preferred embodiments of the invention and the mannerof practicing the same.

Referring to the drawing,

Figure 1 is a View of a rotating anode embodying my present invention,and its cooperating cathode as applied in an X-ray generator;

Figure 2 is a sectional view taken through an anode of the stationarytype; and

Figures 3 and 4 are sectional views through molds in which the anodesshown in Figures 1 and 2 may be fabricated as castings.

To illustrate my invention, I have shown in the drawing anode means I lcomprising a copper alloy body, the material of which embodies certaindesirable characteristics hereinafter more fully described, said bodycarrying target means l3 imbedded therein. The anode means and itstarget are adapted to be enclosed in an evacuated, usually glass,envelope, together with cathode means l5, so that by electricallyenergizing the anode and cathode, X-rays may be generated in accordancewith known principles.

As shown in Figure 1, the cathode l5'may comprise a filament l1 suitablymounted in a'focusing cup [9 disposed in position to direct a stream ofelectrons upon the target l3. The anode means II, as shown in Figure 1,may comprise a disk 2| carrying the target I3 in the form of an annularband 23 imbedded in the peripheral portions of the disk 2|, said disk 2|being mounted for rotation on a suitable shaft or stem 25 by thefastening means 21.

My invention, however, is not necessarily restricted to an anode of therotating type shown in Figure 1, and may simply comprise a preferablycylindrical body 29 comprising a copper alloy having the desiredcharacteristics hereinafter described more fully, the body 29 having aninclined face 3| in which the target means I3 is imbedded.

It should be understood that the impingement of electrons, emitted bythe cathode l5, upon the target l3 for the production of X-rays, causesthe generation of substantial amounts of heat in the anode. I haveobserved that ordinary copper, which has an annealing orrecrystallization temperature of 0., when utilized as a material for theformation of the body of the anode, does not resist in satisfactorymanner the temperatures to which the anode is thus subjected in service.Ordinary copper and other anode materials have a tendency toward thedevelopment of cracks in the body of the anode due, in part, to graingrowth and uneven heating and cooling. The cracks usually initiallyoccur adjacent the target [3, in the vicinity of which the body is atmaximum temperature, the cracks spreading thence throughout the body ofthe anode. Such cracks insulate the body'against the free passage ofheat therethrough and prevent the heat generated at the target fromdissipating by conduction through the anode body to such an extent thatthe target becomes burned and useless. V

The development of cracks is particularly noticeable in rotating anodesin which the size and mass of the anode body, and consequently its heatdissipating ability, is made as small as possible, due to the rotatingcharacter of the anode and the necessity of maintaining the rotatingmass as small as possible. In stationary anodes of the type illustratedin Figure 2, the problem of anode cracking is also present, although toa lesser degree than in rotating anodes, since a stationary anode may bedesigned with more nearly adequate heat conducting sectional areas thanis the case in rotating anodes.

The development of grain growth in copper alloy anodes under the actionof heat in service results in the cracking of the anode base. Thedevelopment of such cracks provides heat insulation, thus preventing theanode from transmitting and dissipating the heat generated at the targetas rapidly as it should. Under such circumstances, the target may becomeoverheated, with resulting pitting and cracking, thereby rendering thesame useless.

Anode cracks may develop in position extending longitudinally throughthe body of the anode, thus providing gas leak paths through the crackedanode communicating the interior of the lamp envelope with its exteriorin structures where the anode is sealed in the envelope by aglass-to-metal seal, thus also rendering the entire device inoperativedue to gas leakage therein through such cracks.

An anode for an X-ray generator, whether ofthe stationary or rotatingtype, may be fabricated by casting the anode material in a suitable moldin which has been anchored the target means [3. In Figure 3 of thedrawing, I have shown a mold for casting an anode of the stationarytype, said mold comprising suitable walls 33 and an inclined bottom 35formed with a socket 31 for receiving the target means I3. The targetmeans 13 may comprise any suitable material, preferably tungsten,although platinum, rhenium, uranium, and other metals, may be employed.

The target means preferably comprises a ma- 1 terial having a highmelting point and may comprise any of the metals having an atomic numberfalling between '72 and 92, and rhenium and tungsten for practicalreasons are preferred.

The principal advantage of rhenium over tungsten is than rhenium isductile and therefore has less tendency to develop cracks when subjectedto excessive high temperatures as at the focal spot in the target of anX-ray generator, and a rhenium target will successfully resisttemperatures substantially in excess of the temperatures at whichtargets comprising tungsten fail. Tungsten is a non-elastic substance,so that when the focal spot becomes overheated, as by the de velopmentof cracks in the base and consequent failure of heat dissipation, thetarget itself tends to crack at the marginal edge of the focal spot.

For an anode of the stationary type, the target means may be formed as adisk-like button, the anode means [3 for a rotating anode comprising anannular band, as clearly shown in Figure 1. It is ordinarily necessary,in casting the anode material upon the target means, to anchor thelatter upon the bottom of the mold in which the anode is cast, in orderto prevent the displacement of the target means in the mold, and to thisend I have shown, in Figure 3, the target means l3 anchored in place bymeans of holding wires 39 applied through suitable perforations in thecasting mold and having ends bent over upon the target means in themold, the remote ends of the wires extending outwardly through theopenings in the mold and being bent outwardly thereof to retain thesame, and the target means, in place. After the anode body has beenformed as a casting in the mold, the formed anode may be removed, andthe outer portions of the holding wires 39 may be snipped off.

The present invention contemplates the fabrication of the body [I of theanode of a heat treatable copper alloy having high conductivity andhardness, and a relatively high annealing or recrystallizationtemperature; and I have developed a predominantly copper alloy, havingchromium as an alloy constituent, that affords a satisfactorycrack-resisting anode material having the foregoing desiredcharacteristics.

The chromium constituent preferably comprises a quantity of chromium ofthe order of 0.5 per cent. This crack-resisting alloy may be fabricatedto form an anode by casting the same, in molten state, upon the targetmeans l3 which preferably comprises a preformed piece of tungsten,rhenium or other suitable target material. I have encountered difiicultyin causing the copper-chromium alloy to weld to the target materialbecause the alloy does not readily wet the target material, especiallyif the same comprises tungsten. In order to enable the alloy to wet thetarget material, I may add, as an alloy ingredient, a suitabledeoxidizing agent, such as beryllium, lithium, boron or calcium, and forthis purpose beryllium particularly, and lithium, are especially welladapted. The deoxidizing medium may and preferably does compriseapproximately 1 per cent of the total alloy constituents. A satisfactoryformula is:

Per cent by weight Copper 98.5 Beryllium 1.0 Chromium 0.5

The heat treating schedule to which I preferably subject the alloy, inorder to produce the desired hardness, conductivity and non-crackingcharacteristics, contemplates the heating of the material to at least900 C., which, of course, may be accomplished as a step in the initialformation of the alloy, if desired, or in melting the alloy for castingthe same in a mold or die. The alloy should then be cooled rapidly, andthe cooling operation should be sufliciently rapid to preserve thechromium constituent for precipitation between the grain boundaries inthe casting during the subsequent hardening operation. Unless thecasting is cooled rapidly, the chromium constituent tends to escape fromthe casting, partly by evaporation, but mostly by migration to thesurface of the casting where the chromium constituent becomes oxidized.After being rapidly cooled, as aforesaid, the alloy may then be hardenedby heating at 500 C. for from two to four hours, depending upon the sizeof the piece.

Under ordinary circumstances, cooling by quenching in water would besatisfactory from the standpoint of rapidity of cooling, but quenchingin water tends to damage the target means l3 if the same comprisestungsten.

In accordance with my present invention, the alloy is cast into the moldand around the target means l3 in a vacuum casting furnace of standardconstruction, and is therefore cooled under vacuum at a ratesufliciently rapid to preserve the chromium constituent as aforesaid.

After the casting has thus been cooled in the casting furnace, it may beand preferably is immediately assembled, without further treatment, intheenvelope of an X-ray tube and is there subjected for several hours toa bakeout process at approximately 500 C., while the tube envelope isconnected with an exhaust pump. During the bakeout process, the anodemay be subjected to electrical bombardment, and this bombardment,together with the bakeout process, provides suflicient heat treatment at500 C. to actually increase the hardness of the anode by causing theprecipitation of chromium between the grain boundaries in the casting.

Precipitation of chromium in this fashion, by heat treatment at 500 C.,not only increases the hardness of the alloy but also increases itstensile strength. After heat treatment, the allow has an annealingtemperature of the order of 500 C., that is to say, no grain growth ordecrease in .hardness will occur so long as the temperature of the anodeis not allowed to exceed 500 C.

Embodied in an X-ray generator, the anode may safely develop operatingtemperatures of the order of 400 C. and up to a maximum of 500 0.,without danger of failure due to cracking; and the alloy has heatconducting ability equal to 75 per cent that of copper at roomtemperature, and 90 per cent that of copper at 400 0., being thussubstantially ideal for the purpose herein described. While hardness isa desirable characteristic, high heat conductivity is essential in orderto permit rapid dissipation of heat from the point of generation thereofat the target, thus ruling out other alloys of copper that are ofsuperior hardness and having higher annealing temperatures. vIt isessential not only to utilize a material having a relatively highannealing temperature to inhibit grain growth at the operatingtemperatures to which the anode is subjected in service, but also toprovide a material having high heat conductivity.

It is thought that the invention and numerous of its attendantadvantages will be understood from the foregoing description, and it isobvious that numerous changes may be made in the form, construction andarrangement of the several parts with-out departing from the spirit orscope of the invention, or sacrificing any of its attendant advantages,the form herein described being a preferred embodiment for the purposeof illustrating the invention.

The invention is hereby claimed as follows:

1. An anode comprising a stem of predominantly copper allow containing ahardening material as an alloy constituent in quantities of the order of0.5 per cent, said alloy having a recrystallization temperature inexcess of 400 C. and having heat conducting ability in excess of 50 percent of that of pure copper at room temperature, and having hardness inexcess of 50 Rockwell E scale.

2. An anode comprising a stem of copper alloy including a hardeningmaterial of the class including chromium and cobalt in quantities of theorder of 0.5 per cent as an alloy constituent and adapted for heattreatment to harden the same by precipitation of the hardeningconstituent between grain boundaries in the material.

3. An anode comprising a stem of copper alloy including chromium inquantities of the order of 0.5 per cent as an alloy constituent andadapted for heat treatment to harden the same by precipitation of thechromium between grain boundaries in the material.

4. An anode comprising a stem of copper alloy including cobalt inquantities of the order of 0.5 per cent as an alloy constituent andadapted for heat treatment to harden the same by precipitation of thecobalt between grain boundaries in the material.

5. An anode comprising a stem of predominantly copper alloy comprisingchromium as an alloy constituent in quantities of the order of 0.5 percent.

6. An anode comprising a stem of predominantly copper alloy comprisingcobalt as an alloy constituent in quantities of the order of 0.5 percent.

7. An anode comprising a stem of predominantly copper alloy containing,as alloy constituents, a hardening material in quantities of the orderof 0.5 per cent and a deoxidizing agent in quantities of the order of 1per cent, said alloy having a recrystallization temperature in excess of400 C, and having heat conducting ability in excess of 50 per cent ofthat of pure copper at room temperature and having hardness in excess of50 Rockwell E scale.

8. An anodecomprising a stem of predominantly copper alloy including ahardening agent of the class including chromium and cobalt inquantitiesof the order of 0.5 per cent, together with a (is-oxidizingagent of the class including beryllium, lithium, calcium and boron inquantities of the order of 1 per cent, whereby to improve the Wettingcharacteristics of the alloy.

9. An anode comprising a stem of predominantly copper alloy comprisingchromium .as an alloy constituent in quantities of the order of 0.5 percent, togetherwith beryllium as a wetting agent in quantities of theorder of 1 per cent.

10. An anode comprising a stem of predominantly copper alloy comprisingchromium as an alloy constituent in quantities of the order of 0.5 percent, together with lithium as a wetting agent in quantities of theorder of 1 per cent.

11. An anode comprising a stem of predominantly copper alloy comprisingchromium as an alloy constituent in quantities of the order of 0.5 percent, together with calcium as a wetting agent in quantities of theorder of 1 per cent.

12. An anode comprising a stem of predominan ly copper alloy comprisingchromium as an alloy constituent in quantities of the order of 0.5 percent, together with boron as a wetting agent in quantities of the orderof 1 per cent.

13. An anode comprising a stem of predomi-, nantly copper alloycomprising cobalt as an alloy constituent in quantities of the order of0.5 per cent, together with berylliumas a wetting agent in quantities ofthe order of 1 per cent.

14. An anode comprising a stem of predominantly copper alloy comprisingcobalt as an alloy constituent in quantities of the order of 0.5 percent, together with lithium as a wetting agent in quantities of theorder of l per cent.

15. An anode comprising a stem of predominantly copper alloy comprisingcobalt as an alloy constituent in quantities of the order of 0.5 percent, together with calcium as a wetting agent in quantities of theorder of 1 per cent,

16. An anode comprising a stem of predominantly copper alloy comprisingcobalt as an alloy constituent in quantities of the order of 0.5 percent, together with boron as a wetting agent in quantities of the'orderof 1 per cent,

17. An anode comprising a stem of predominantly copper alloy containinga hardening material as an alloy constituent in quantities of the orderof 0.5 per cent, said alloy having a recrystallization temperature inexcess of 400 C. and having heat conducting ability in excess of 50 percent of that of pure copper at room temperature and having hardness inexcess of 50 Rockwell E scale, and a target integrated in the said stemand comprising a metal of the class having an atomic number within therange 72-92 and including tungsten, platinum, rhenium and uranium.

. 18. An anode comprising a stem of predominantly copper alloy includinga hardening agent of the class including chromium and cobalt inquantities of the order of 0.5 per cent as an alloy constituent,together with a deoxidizing agent of the class including beryllium,lithium, calcium and boron to improve the wetting characteristics of thealloy, and a target integrated with said stern and comprising a metal ofthe class having an atomic number within the range 72-92 and includingtungsten, platinum, rhenium and uranium.

19. An anode comprising a stem of predominantly copper alloy comprisingchromium as an alloy constituent in quantities of the order of 0.5 percent, together with beryllium as a wetting agent in quantities of theorder of 1 per cent, and a target comprising a metal of the class havingan atomic number within the range 72-92 and including tungsten,platinum, rhenium and uranium integrated on the stem in intimate heattransferring relationship therewith, said stem being configurated torapidly dissipate heat generated at said target.

20. An anode comprising a stem of predominantly copper alloy comprisingchromium as an alloy constituent in quantities of the order of 0.5 percent, together with lithium as a wetting agent in quantities of theorder of 1 per cent, and a target comprising a metal of the class havingan atomic number within the range 72-92 and including tungsten,platinum, rhenium and uranium integrated on the stem in intimate heattransferring relationship therewith, said stem being configurated torapidly dissipate heat generated at said target.

21. An anode comprising a stem of predominantly copper alloy comprisingchromium as an alloy constituent in quantities of the order of 0.5 percent, together with calcium as a wetting agent in quantities of theorder of 1 per cent, and a target comprising a metal of the class havingan atomic number within the range 72-92 and including tungsten,platinum, rhenium and uranium integrated on the stem in intimate heattransferring relationship therewith, said stem being configurated torapidly dissipate heat generated at said target.

22. An anode comprising a stem of predominantly copper alloy comprisingchromium as an alloy constituent in quantities of the order of 0.5 percent, together with boron as a wetting agent in quantities of the orderof 1 per cent, and a target comprising a metal of the class having anatomic number within the range 72-92 and including tungsten, platinum,rhenium and uranium integrated on the stem in intimate heat transferringrelationship therewith, said stern being configurated to rapidlydissipate heat generated at said target.

23. An anode comprising a stem of predominantly copper alloy comprisingcobalt as an alloy constituent in quantities of the order of 0.5 percent, together with beryllium as a wetting agent in quantities of theorder of 1 per cent, and a target com-prising a metal of the classhaving an atomic number within the range 72-92 and including tungsten,platinum, rhenium and uranium integrated on the stem in intimate heattransferring relationship therewith, said stem being configurated torapidly dissipate heat generated at said target.

24. An anode comprising a stem of predominantly copper alloy comprisingcobalt as an alloy constituent in quantities of the order of 0.5 percent, together with lithium as a wetting agent in quantities of theorder of 1 per cent, and a target comprising a metal of the class havingan atomic number within the range 72-92 and including tungsten,platinum, rhenium and uranium integrated on the stem in intimate heattransferring relationship therewith, said stem being configurated torapidly dissipate heat generated at said target.

25. An anode comprising a stem of predominantly copper alloy comprisingcobalt as an alloy constituent in quantities of the order of 0.5 percent, together with calcium as a wetting agent in quantities of theorder of 1 per cent, and a target comprising a metal of the class havingan atomic number within the range 72-92 and including tungsten,platinum, rhenium and uranium integrated on the stem in intimate heattransferring relationship therewith, said stem being configurated torapidly dissipate heat generated at said target.

26. An anode comprising a stem of predominantly copper alloy comprisingcobalt as an alloy constituent in quantities of the order of 0.5 percent, together with boron as a wetting agent in quantities of the orderof 1 per cent, and a target comprising a metal of the class having anatomic number within the range 72-92 and including tungsten, platinum,rhenium and uranium integrated on the stem in intimate heat transferringrelationship therewith, said stem being configurated to rapidlydissipate heat generated at said target.

27. An anode comprising a stem of predominantly copper alloy containinga hardening material as an alloy constituent in quantities of the order,of 0.5 per cent, said alloy having a recrystallization temperature inexcess of 400 C. and having heat conducting ability in excess of 50 percent of that of pure copper at room temperature and having hardness inexcess of 50 Rockwell E scale, and a target integrated in the said stemand comprising rhenium.

28. An anode comprising a stem of predominantly copper alloy containing,as alloy constituents, a hardening material in quantities of the orderof 0.5 per cent and a deoxidizing agent in quantities of the order of 1per cent, said alloy having a recrystallization temperature in excess of400 C. and having heat conducting ability in excess of 50 per cent ofthat of pure copper at room temperature and having hardness in excess of50 Rockwell E scale, and a target integrated in the said stemandcomprising rhenium.

29. An anode comprising a stem of copper alloy including a hardeningmaterial of the class including chromium and cobalt in quantities of theorder of 0.5 per cent as an alloy constituent and adapted for heattreatment to harden the same by precipitation of the hardeningconstituent between grain boundaries in the material, and a targetintegrated in the said stem and comprising rhenium.

30. An anode comprising a stem of predominantly copper alloy including ahardening agent of the class including chromium and cobalt in quantitiesof the order of 0.5 per cent as an alloy constituent. together with adeoxidizing agent of the class including beryllium, lithium, calcium andboron to improve the wetting characteristics of the alloy, and a targetintegrated with said stem and comprising rhenium.

ZED J. ATLEE.

